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发表于 2012-6-10 21:29
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本帖最后由 恭喜发财 于 2012-6-10 22:30 编辑
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Introduction of energy efficient homes
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6 T5 B) u6 }+ Q% iEnergy efficiency is the most important consideration in green buildings design. Leadership in Energy and Environment (LEED) certification, the largest green building rating system in North America, organizes its evaluation criteria into five environment categories: sustainable sites, water efficiency, energy and atmosphere, materials and resources, and indoor environmental quality. Development density, community connectivity and public transportation access are three major considerations in sustainable site selection. An in-fill project in an existing urban community obviously has much less impact on environment than a home built in a new developed subdivision at the perimeter of the city. The intent to increase water efficiency is to reduce the burden on municipal water supply and wastewater systems. The easiest way to do that is using low flash toilets, low flow showerheads and faucets. In materials and resources areas, a green home need to be designed and constructed in a manner that minimizes wastes hauled and disposed of in landfills. Extending the lifecycle of existing building stock and using recycled or recyclable materials are two potential strategies to achieve this goal. Indoor air quality directly contributes to the comfort and well-being of the occupants. Since green homes are often very airtight, ventilation systems must be designed to meet or exceed the minimum requirements on outdoor air ventilation rates. Other measures to improve indoor air quality include using low-VOC materials for adhesives, sealants, paints and flooring systems, and installing better air filters (≥ MERV 10). Improving the overall energy performance has the heaviest weight in green home rating system. It directly contributes to reducing energy consumption and carbon dioxide emissions. In Canada, residential sector is responsible for more than 17% of total primary energy consumption and for 16% of greenhouse air emissions.1 w1 B7 q" g- _, N& Q
) ^3 l/ [/ u4 O) YThe home energy efficiency has been improved gradually in the past. Today’s house is about 50% more energy efficient than the house built 50 years ago. Measured by EnerGuide rating, a house built in 50s or 60s can be rated about 55, a house built in 70s rated 60, a house built in 80s and early 90s rated about 65, and a typical house built today will be at 70-72 level. As a government regulated system, EnerGuide rate home’s energy efficiency on a scale of 0 to 100. A rating of 0 represents a home with major air leakage, no insulation and extremely high energy consumption. A rating of 100 represents a house that is airtight, well insulated, sufficiently ventilated and requires no purchased energy on an annual basis. Every point increase in rating is equivalent about 5% energy efficiency improvement.
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; _: z/ q! n9 W8 j: C% t3 QIf a house gets EnerGuide rating of or above 80, people normally consider it as energy efficient home. It means that the house only consumes about 60% of energy that a same house built to today’s industry standard does. A house that achieves EnerGuide 86 will consume about 40% of energy, and meets the minimum energy conservative requirement of NetZero Homes. A NetZero home still consumes energy, however at the same time, it generates equal or more energy from solar or others renewable resources. The first five NetZero homes in Alberta were built in 2008 under CMHC’s (Canada Mortgage and Housing) Equilibrium program. Some detailed information about three NetZero homes built in Edmonton can be found through Green Edmonton website (http://greenedmonton.ca).
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For a typical home in Alberta, most of the energy usage goes towards space heating, accounting to about 63% of the entire energy consumption. The second largest energy use in a home is hot water, about 18%. The energy consumption of appliances is about 13% and lighting 4%. From the above analysis, it is easy to see that the priority in improving home energy efficiency is to reduce heat loss from building envelope (wall, ceiling, floor and windows), from air ventilation, and from hot water. Some major systems affecting building energy performance include:8 J; S+ w0 k @! }$ k! V
Building envelope: Air tightness and insulation value) Q2 S2 P3 K4 k B! ?
Windows and doors: overall U value and glazing SHGC (Solar Heat Gain Coefficient)0 @6 B) P, P- o2 K; L2 O
HVAC: furnace size, efficiency and location; duct tightness, distribution efficiency
2 y% `1 T' }' {# j( T: \. L5 t& C% qHot Water: Generation, distribution and stand-by-losses; n4 j% v3 _. W) H1 U
Appliances: Stove and oven, refrigerator, dishwasher, washer & dryer8 `7 n$ n/ G5 y* h! _
Lighting and miscellaneous: Phantom load is about 10% of electricity usage.
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There is a free software, HOT 2000, that can help us to calculate the annual energy consumption for a home. It is developed by Resources Canada and downloaded at following link http://canmetenergy.nrcan.gc.ca/eng/software_tools/hot2000.html. This software is well recognized by governments as the base of energy efficient home grant and incentive application.
: w3 X8 d: q1 d7 N, pLet’s use a typical 2000 square feet single-family detached house as an example to explain how much energy a home consumes in a year and how much savings an energy efficient house can have on utilities’ bill. A 4-person family living at average life style in the house typically consumes 140 GJ of natural gas and 9,600 kWh of electricity. The utilities’ bill is about $2800 per year, including $875 grid-connection charges. An energy efficient home with EnerGuide rating of 80 consumes 75 GJ of natural gas and 8,760 kWh of electricity per year and pays utilities’ bill about $2250. A Net Zero home generally does not have natural gas connection and consumes 12,000 kWh of electricity, but it also generates the same amount energy from solar PV or other renewable energy generation systems. Considering that it still need to pay electricity connection charge and delivery fee, the annual utilities’ bill is about $500.( j5 b5 q, q8 D; a
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When you improve your house energy efficiency, the most cost-effective way is to seal the house (reduce air leakage) and increase insulation in building envelope. The insulation in exterior wall is usually R20 for houses built after 90’s and R12 before. However, since the insulation is installed between the studs and wood is not a heat resistant material, the R value of a 2x6 exterior wall is about R15-16. Considering convection caused by air leakage, the actual R value in cold weather condition will go much lower. Spray foam insulation is very effective in reducing air leakage and rigid exterior insulation is commonly used to mitigate the thermal bridging effect at wood studs. The minimum artic insulation requirement is R28 and usually we use R40 for new homes. The energy efficient home requires R51 and NetZero home R90. Building Code does require basement floor insulation. However, we know the soil around basement remains 5°C year around. Therefore, we suggest adding a minimum insulation of R5 (EPS or XPS) under the basement floor. The R value of normal due-pane window is about 2-3, and a triple glaze LOW-E window can get R5. It is also a good choice to increase the energy efficiency of the house.; h7 d9 G( h; ?. \6 e
) D7 x$ E+ R' s, b9 F E0 IReplacing old hot water tank and furnace with high energy efficient ones also have good payback. Using Energy Star appliances are is another thing that is very easy to do and has good effect. If you want to do further, you can try to add heat recovery ventilation (HRV), domestic hot water recovery (DHWR). If you want to build a NetZero home, you need to consider energy generation technologies, such as solar PV and geothermal systems. Life style has big impact on energy consumption. For instance, if a family member uses hot-tub three times a week, this family will use more hot water and more energy. The goal for energy efficient house is not to compromise personal life style but to minimize its impact to home’s energy performance.
" P+ R* |6 V. i' P) Q7 A6 [7 `Today, our society pays more and more attention on the environmental and sustainable development. We hope this article can help you get some ideas of green housing and you can use some tips introduced in the article. To leave a better world for our grandchildren, we all have responsibility to make the environment better and reserve resources for them. ) {4 ?9 ]# V* x. `; M
+ D' A+ e+ Q6 A+ Q( NAlberta Chinese Construction Association
9 Q. _4 H9 P3 v/ k% sDr. Yu Haitao, Yin, Zhimin6 _* O% U: B4 D2 q( X0 x) u( Y( v
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发表于 2012-6-10 21:08
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黄教授说得好！环保住宅只不过是又一个向人民榨取钱财的项目罢了。5 c' F3 [; U- t
节能。环保。